The GOLD project is a mission of
opportunity and part of NASA’s Explorer Program, designed to
provide frequent, low-cost access to space for heliophysics and
astrophysics missions with small to mid-sized spacecraft. The mission
is a collaboration between LASP (Laboratory for Atmospheric and Space
Physics) at the University of Colorado in Boulder, CO, UCF (University
of Central Florida) in Orlando, FL, and the commercial communications
satellite company, SES-GS (Government Solutions), Reston, VA. Note: In
2011, SES-GS was introduced as part of the global SES family. 1)2)3)4)5)

UCF was awarded a $55 million NASA
grant to build and launch into space an instrument the size of a
microwave oven that will provide unprecedented imaging of the
Earth’s upper atmosphere. The award is the largest single grant
in UCF’s history, and UCF will become the first Florida
university to lead a NASA mission. 6)

GOLD is a NASA Explorer mission of
opportunity to build and launch an instrument to provide unprecedented
imaging of the Earth’s upper atmosphere from a geostationary
orbit. The information collected by the GOLD mission will have a direct
impact on understanding space weather and its impact on communication
and navigation satellites, which we’ve come to rely on for
everything from television programming to cell phone coverage and GPS
in our vehicles.

In addition to providing the compact
instrument, LASP will provide project management, systems engineering,
safety and mission assurance, instrument operations, and Education and
Public Outreach (E/PO) for the mission. Under the leadership of GOLD PI
(Principal Investigator) Richard Eastes of UCF, UCF will oversee the
project, and build the data center that will collect, process, and
distribute the science data for the mission.

An important aspect of the mission is that GOLD will be one of the first NASA science missions to fly as a hosted payloadon a commercial communications satellite.
This is by far the most cost-effective way to put a science instrument
into geostationary orbit, where it can observe nearly a full hemisphere
of the Earth all of the time.

The goal of the GOLD imaging mission
is the study of the boundary layer between Earth and space and to
address four primary science questions:

1) How do geomagnetic storms alter the temperature and composition structure of the thermosphere?

2) What is the global-scale response of the thermosphere to solar extreme-ultraviolet variability?

3) How significant are the effects of atmospheric waves and tides propagating from below on thermospheric temperature structure?

4) How does the nighttime
equatorial ionosphere influence the formation and evolution of
equatorial plasma density irregularities?

GOLD is a NASA PI (Principal
Investigator) mission, lead by Richard W. Eastes of UCF (University of
Central Florida). UCF will oversee the project and build the data
center that will collect, process and distribute the data for the
mission. LASP will build the compact instrument, which will operate in
a geostationary orbit, and SES-GS is scheduled to launch the hosted
payload on one of its communication satellites in 2017.

Other members of the GOLD team that
will be supporting the mission include NCAR (National Center for
Atmospheric Research), UCB (University of California at Berkeley),
Computational Physics Inc., and NOAA (National Oceanic and Atmospheric
Administration).

SES-14 is a geostationary
communications satellite operating in C- and Ku-bands across the
Americas and the North Atlantic region, which uses electric propulsion
for initial orbit raising and all on-orbit maneuvers. The spacecraft is
being built by Airbus Space and Defence, based on the Eurostar E3000
EOR (Electric Orbit Raising) platform, which exclusively uses electric
propulsion for orbit raising. SES-14 will replace SES's satellite
NSS-806 and add new capacity. 7)

The satellite combining power and
flexibility will have a double mission. The first will be a wide-beam
payload of C- and Ku-band, covering the Americas plus a link to Europe.
The other payload, called HTS (High Throughput Satellite) with numerous
user beams, will combine an on-board processor with multi-beam coverage
of the Americas and the North Atlantic. The Ku-band wide beams will
bring augmented capacity to serve growing video neighborhoods in the
Americas and support existing VSAT services. The HTS Ku-band multi-spot
beams (20) are ideal for traffic-intensive data applications such as
mobile backhaul, maritime and aeronautical services.

SES-14 will carry seven antennas. It
will have a take-off weight of 4,200 kg and an electric power of 16 kW.
The satellite is scheduled for launch in late 2017 and its electric
propulsion system will enable it to reach geostationary orbit in four
months, depending on the type of launcher used.

Electric propulsion makes it
possible to reduce the mass of satellites, leading to lower launch
costs for a given mission and/or a more capable satellite for a given
mass. Airbus Defence and Space has been using electric propulsion for
station keeping for more than ten years, and is building the first
large satellites using only electric propulsion for initial orbit
raising. 8)

GOLD will transmit data from a
geostationary orbit at a fast pace, to build up a full-disk view every
half hour, providing detailed large-scale measurements of the response
of the upper atmosphere to forcing from the Sun, the magnetosphere, and
the lower atmosphere.

Hosted GOLD payload:

Flying as a hosted
payload on a commercial communications satellite, GOLD takes advantage
of the resource margins available in the early years of the commercial
mission’s planned 15-year life. This hosted payload approach is a
pathfinder for cost-effective NASA science missions. 9)

The affordable ride to GEO makes it
possible for an Explorer-class Mission of Opportunity to perform FUV
(Far UltraViolet) imaging of nearly a complete hemisphere on a
30-minute cadence. This global-scale, high-cadence imaging will enable
GOLD to distinguish between spatial and temporal variations in the TI
(Thermosphere Ionosphere) system caused by geomagnetic storms,
variations in solar EUV, and forcing from the lower atmosphere.

The most significant difference
between developing instrumentation for a NASA-owned mission and
accomplishing the same task for a commercial satellite is that
communications satellites are procured on a faster schedule - 24 to 36
months from satellite contract to launch - than the instrument
development. GOLD has partnered with SES Government Solutions (SES-GS),
the comsat mission owner-operator, to define instrument interfaces and
requirements that will be included in the eventual Request for Proposal
to candidate spacecraft vendors. SES-GS launches 3 to 4 missions per
year, which allows the GOLD-SES-GS partnership to match the
instrument’s launch readiness date with a suitable mission.

Figure 5: Artist's rendition of
the SES-14 coverage; the hosted payload GOLD will examine the response
of the upper atmosphere to forcing from the Sun, the magnetosphere and
the lower atmosphere (image credit: NASA) 10)

Development status:

• December 22, 2017: SES-14 has
arrived safely at the Guiana Space Center in Kourou, French Guiana, in
preparation for launch by an Ariane 5 vehicle in January 2018. 11)

- SES-14 was built by Airbus
Defence and Space and is an electric satellite. It will rely fully on
electric propulsion and will be equipped with an electric plasma
propulsion system for orbit raising and in-orbit maneuvers. The new
spacecraft also features a Digital Transparent Processor (DTP), which
increases payload flexibility and will provide customized bandwidth
solutions to SES’s customers.

Figure 6: The
GOLD instrument (the gray and white object located on the front right
corner of the top deck) has completed environmental testing and is
shown here on the SES-14 spacecraft in preparation for a scheduled
January 2018 launch date (image credit: Airbus DS) 12)

- Marking a significant milestone
in the lead up to launch, GOLD was integrated onto the SES-14 satellite
in preparation for a series of environmental tests at Airbus Defence
and Space in Toulouse, France. Airbus DS is building the SES-14
satellite for SES-GS.

Figure 7: The
GOLD instrument is hoisted up and installed onto the SES-14 commercial
communications satellite, which is being assembled at Airbus Defence
and Space in Toulouse, France (image credit: Airbus DS)

• January 4, 2017: A NASA
instrument that will study the upper atmosphere and the impact of space
weather on Earth is a step closer on its journey into space. The
LASP-built instrument was shipped to Airbus Defence and Space in
Toulouse, France, for integration on the SES-14 communications
satellite. 15)

- GOLD is a pathfinder for
NASA’s use of commercial spacecraft for science missions. UCF and
LASP partnered with SES Government Solutions (SES-GS), based in Reston,
VA, to provide GOLD with its ride into geostationary orbit on the
SES-14 satellite that is owned and operated by SES, the parent company
of SES-GS.

• December 1, 2016: Photo of the GOLD science team and the GOLD instrument. 16)

Figure 9: Members of the GOLD
science team gather with the instrument in a LASP clean room on
December 1, 2016, just after the instrument went through its pre-ship
review ahead of shipment to Airbus Defence and Space in Toulouse,
France (image credit: LASP)

Launch: The GOLD payload was
launched as a hosted payload on the SES-14 communication satellite of
SES-GS (SES Government Solutions) on 25 January 2018 (22:20 UTC).
SES-14 was built by Airbus DS. The launch vehicle was Ariane-5 ECA and
the launch complex was ELA-3 in Kourou (flight VA241). - The second
communication satellite on this flight was Al Yah-3 of Yahsat. Built by
Orbital ATK, Al Yah-3 will support broadband Internet and data services
over Africa and Brazil for Yahsat Satellite Communications Company of
Abu Dhabi.

According to Arianespace, a few
seconds after ignition of the upper stage, the second tracking station
located in Natal, Brazil, did not acquire the launcher telemetry. This
lack of telemetry lasted throughout the rest of powered flight.
Subsequently, both satellites were confirmed separated, acquired and
they are on orbit. SES-14 and Al Yah 3 are communicating with their
respective control centers. Both missions are continuing. 17)

Both satellites,
SES-14 and Al Yah-3, use all-electric propulsion for orbit raising in
GTO (Geosynchronous Transfer Orbit) and in-orbit maneuvers.

The University of Colorado announced
in April 2015 that it had awarded a five-year contract to SES- GS VA,
to host a NASA-funded science instrument on board SES-14, a
communications satellite to be stationed over the Americas. 18)

The contract award, made by the
University of Colorado, a partner in the project, will give the GOLD
payload the ride it needs to geostationary orbit on board SES-14, a
communications satellite to be stationed over the Americas. From there,
the microwave-sized device will transmit data of how Earth’s
upper atmosphere responds to solar impacts back to scientists for
analysis. 19)

SES-14 will fulfill two primary
missions: its C-band wide beams are specifically designed for SES's
expanding cable neighborhood in Latin America, while its Ku-band HTS
spot beams will provide expansion capacity to serve the dynamic
aeronautical and maritime markets and other traffic-intensive
applications, such as cellular backhaul or broadband delivery services.

With the launch of Al Yah-3,
Yahsat's commercial Ka-band coverage will be extended to an additional
20 markets, reaching 60% of Africa's population and over 95% of
Brazil's population. - Al Yah-3 will be positioned at 20 West
Longitude.

The Al Yah-3 satellite carries 53
active Ka-band user beams and four gateway beams, and produces
approximately 8.0 kW of payload electrical power. The Ka-band spot
beams provide two-way communications services to facilitate high-speed
delivery of data to end-user applications such as broadband Internet
and corporate networking as well as IP backhaul for telecommunications
service providers.

Al Yah-3 was built by Orbital ATK using its new GEOStar-3 hybrid platform, the first application of this platform.

Mission status

• December 26, 2019: High above
the Earth, there is a dynamic region where the atmosphere meets space.
Home to astronauts on the space station and to many Earth-observing and
commercial satellites, the ionosphere
constantly fluctuates and responds to changes from above and below. A
NASA-funded instrument is shedding new light on the invisible processes
and rhythms at play in this intersection between Earth and space. 20)

- Between 80 and 600 km above the
ground, radiation from the Sun cooks some of the gases in our upper
atmosphere until they lose an electron or two. The result is a sea of
electrically charged particles—ions—intermingled with the
neutral upper atmosphere. Energy is constantly streaming in from the
Sun and from near-Earth space, an expression of what scientists call space weather.
But the ionosphere also responds to weather patterns that ripple up
from the lower parts of Earth’s atmosphere. Such changes can make
it challenging to work in space, and they regularly affect key
communications systems such as high-frequency (HF) radio and GPS.

- According to atmospheric
scientist Richard Eastes of the University of Colorado, the region is
far more variable than scientists expected. That insight comes from
work with the Global-scale Observations of the Limb and Disk (GOLD)
instrument, which images the ionosphere in ultraviolet light to track
changes in temperature, density, and composition.

Figure 10: Satellites are
shedding new light on the invisible processes and rhythms at play at
the intersection between Earth and space. This image was acquired by
GOLD on December 19, 2018—a view of the entire Western Hemisphere
as observed from geostationary orbit.
The left third of the sphere is still in daylight, while eastern North
and South America were bathed in twilight or darkness. The blue strips
stretching across the Atlantic Ocean are known as the Appleton anomaly, a region of the ionosphere around the magnetic equator that stays activated for much of the night due to plasma
rising from lower parts of the ionosphere (image credit: NASA Earth
Observatory, image courtesy of Stanley Solomon and John Correira, GOLD
Project. Story by Lina Tran, NASA Goddard Space Flight Center, with
Mike Carlowicz)

- Eastes noted
that on one night, the crests may be evenly spaced over the equator;
the next night, they can be far apart and in an entirely different
position. The paths that radio waves take—such as those used by
GPS—depend on the density of the ionosphere. Sometimes changes in
the density and location of these hot spots can interfere with
communications signals.

Figure 11: This image pair shows
changes in the composition of the neutral atmosphere over the Western
Hemisphere in full daylight, before and during a geomagnetic storm on
November 4-5, 2018. Note how the ratio of atomic oxygen to nitrogen gas
increases at low latitudes (becoming brighter in the image) and
decreases at high latitudes (darker) in the wake of the storm (image
credit: NASA Earth Observatory, image courtesy of Stanley Solomon and
John Correira, GOLD Project. Story by Lina Tran, NASA Goddard Space
Flight Center, with Mike Carlowicz)

- During such storms, the neutral atmosphere near the magnetic poles is heated by energy coming from the magnetosphere,
and the density ratio decreases rapidly and dramatically. At lower
latitudes, the opposite happens, as large amounts of atomic oxygen move
from high to low latitudes. Since the neutral atmosphere and ionosphere
are coupled, composition changes alter the ionosphere density and the
behavior of radio communications signals.

- Though some features like the
Appleton anomaly are not new to scientists, the GOLD research team was
surprised by how much the ionosphere varies from night to night.
“These were very surprising findings to me, and to the rest of
the team that has been looking at this stuff for many years,”
said Eastes, the principal investigator for GOLD. “It was not
something we anticipated.”

• December 10, 2019: In a Dec.
10 press event at the fall meeting of the American Geophysical Union in
San Francisco, three scientists presented new images of the ionosphere,
the dynamic region where Earth’s atmosphere meets space. Home to
astronauts and everyday technology like radio and GPS, the ionosphere
constantly responds to changes from space above and Earth below. 21)

- The collection of images presented include the first images from NASA’s ICON, new science results from NASA’s GOLD,
and observations of a fleeting, never-before-studied aurora. Together,
they bring color to invisible processes that have widespread
implications for the part of space that is closest to home.

- Earth’s ionosphere
stretches from 50 to 400 miles above the ground and overlaps the top of
the atmosphere and the very beginning of space. Radiation from the Sun
cooks a small portion of gases in the upper atmosphere until they lose
an electron or two. The result: a sea of electrically charged particles
intermingled with the neutral upper atmosphere.

- Besides energy streaming in from
the Sun and near-Earth space, the ionosphere also responds to weather
patterns that ripple up from the lower atmosphere below. These changes
— which can impact astronauts and key communications systems
— are complex and unpredictable. A range of specialized
instruments is key to studying and understanding them.

New GOLD results

- While all-sky cameras provide
views of the ionosphere from the ground, GOLD surveys the region from
geostationary orbit, 22,000 miles above Earth. GOLD Principal
Investigator Richard Eastes, from the University of Colorado, Boulder,
presented new results from the mission: observations that show the
region is far more variable than scientists ever expected.

- GOLD (Global-scale Observations
of the Limb and Disk) is an instrument that images the ionosphere in
far ultraviolet light. This particular wavelength of light is invisible
to our eyes, but useful for tracking changes in the ionosphere’s
temperature, density and composition.

- Since GOLD can see the entire
Western Hemisphere at once, it can observe ionospheric changes and
patterns across the globe. In the past year, GOLD has helped scientists
pin down how the ionosphere responds to geomagnetic storms: Atomic
oxygen increases at low latitudes and decreases at high latitudes,
while molecular nitrogen does the opposite.

Figure 12: In this visualization,
GOLD data is used to show how the ionosphere responded to the July 2
total solar eclipse. On the left (in visible light), the Moon’s
shadow races across South American. On the right, far ultraviolet light
shows nitrogen emissions (video credit: NASA’s Scientific
Visualization Studio/GOLD/Thomas Bridgman/Saurav Aryal)

- GOLD’s unique vantage point
also enabled observations of the July 2 total solar eclipse in South
America. In typical day-night cycles, the pool of electrically charged
atmospheric gases waxes and wanes with the Sun. During the day, the
ionosphere is dense. At night, when the Sun is no longer energizing the
atmosphere, the atmosphere cools. Charged particles gradually
recombine. The ionosphere thins. In a total eclipse, the same thing
happens over a much shorter amount of time. As the July 2 eclipse
crossed over the bottom of South America, scientists were, for the
first time, able to watch this thinning evolve across the Southern
Hemisphere, from space.

Figure 13: The nighttime
ionosphere varies a great deal from night to night. These panels show
the density and shifting location of the nighttime ionosphere between
Oct. 7-25, 2019. Most of the ions are oxygen ions. At night, when they
recombine with electrons, they emit light at a specific wavelength
— 135.6 nm — which GOLD observes. Regions of higher ion
density produce brighter emissions. Radio disturbances often occur when
longitudinal gaps develop, such as the one off the east coast of South
America in the top left image. Why the nighttime ionosphere varies so
much — even during quiet geomagnetic conditions — is not
understood (image credit: NASA/GOLD/Robert Daniell)

- The GOLD
scientists were also surprised by how much the nighttime ionosphere
varies night to night. The paths that radio frequency waves take, such
as those used by GPS, depend on the density of the ionosphere.
Sometimes, changes in the density can interfere with these signals.

- At night, charged particles tend
to settle in crests beside Earth’s magnetic equator. Eastes
likened the images to a T-rex’s toothy grin. On one night, the
crests are evenly spaced over the equator, as if the T-rex is baring
its teeth. The next night, the crests are far apart like the
T-rex’s mouth is open wide, and the night after that, in a
different position entirely. Why the nighttime ionosphere varies so
much is still unclear.

- “These were very surprising
findings to me, and to the rest of the team who’s been looking at
this stuff for many years,” Eastes said. “It’s not
something we anticipated at all.”

• December 7, 2019: Additional
Level 1 data from NASA’s Global-scale Observations of the Limb
and Disk (GOLD) mission are now available via the GOLD website at https://gold.cs.ucf.edu

- Channel A L1C and L1D data are
now available through 11/30/2019. Data will continue to be released on
a regular basis going forward. The dates currently available for each
data product can be found on the Current Data Product Versions page at https://gold.cs.ucf.edu/data/current-data-product-versions/

- Channel B L1C and L1D night time
(NI1) data are also now available through 11/30/2019. The CHB NI1 data
from the period 12/15/18-3/15/19 are available by special request only
through a link on the GOLD download page at https://gold.cs.ucf.edu/data/search/. See section 3.1.5 of the GOLD data release notes for details on the issues with the CHB NI1 data during that time period.

• August 13, 2019: NASA's GOLD
(Global-scale Observations of the Limb and Disk) mission has observed
dramatic and unexplained shifts in the location of features in the
Earth’s ionosphere surrounding the equator. Unanticipated changes
in the nighttime ionosphere can lead to disruptions in communication
and navigation that depend on satellites, such as GPS. 22)

- GOLD is an ultraviolet imaging
spectrograph that was designed and built at the University of Colorado
Boulder’s Laboratory for Atmospheric and Space Physics (LASP) and
is hosted on the SES-14 communications satellite. The latest
discoveries from the mission are challenging mission scientists and
were published last week in Geophysical Research Letters.

Figure 14: This
October 15, 2018, GOLD image of daytime airglow clearly shows the
equatorial ionization anomaly (EIA) as two arcs on either side of the
magnetic equator, which extend across the nightside of the disk. The
colors represent an increase in oxygen emissions from blue to red, with
the left side of the Earth lit by the Sun, which has set over most of
South America (image credit: GOLD)

- Since reaching orbit in October
2018, GOLD has been making observations of the Equatorial Ionization
Anomaly (EIA), regions of the ionosphere with enhanced electron density
north and south of the magnetic equator. One of the primary goals of
the mission is to better understand the behavior of the EIA and the
instabilities within it. GOLD presents a new ability to image the
variability of ionospheric plasma and, ultimately, to understand its
causes.

- “The variability of the
nighttime ionosphere has been a puzzle that scientists have studied for
more decades than most of us have lived,” said Richard Eastes,
GOLD principal investigator and LASP research scientist. “Today
it’s an important problem to solve because better forecasts are
needed for reliable navigation and communication by airplanes and
others.”

- Density variations in the
ionosphere can cause localized plasma depletions called
“bubbles.” Radio waves, including those used for
communications and navigation, can be disrupted when they encounter
these bubbles. The occurrence of bubbles and other ionospheric
irregularities presents a critical challenge for efforts to predict how
changes in solar and geomagnetic activity affect the nighttime
ionosphere.

- Because of GOLD’s unique
perspective from geostationary orbit and its rapid imaging cadence (a
complete scan of each hemisphere every 15 minutes), GOLD is providing
new information that has not been available in previous EIA
observations. From its geostationary vantage some 22,000 miles (35,786
km) above the Earth, GOLD observes the same longitudes repeatedly every
night and provides large scale images of the EIA.

- GOLD has observed gaps occurring
on a majority of the nights and has more irregularly detected abrupt
changes in the location of the EIA. The team will rely on additional
measurements before attempting to determine the cause of variability in
the EIA and its changing location.

- GOLD is a NASA mission of
opportunity managed by the Goddard Space Flight Center in Greenbelt,
MD. The GOLD principal investigator is based at LASP, which built the
instrument, provides project management and systems engineering, as
well as instrument operations for the GOLD mission. GOLD is a hosted
payload on a commercial communications satellite, SES-14, built by
Airbus for Luxembourg-based satellite operator, SES.

• July 17, 2019: In 1972,
Apollo 16 astronauts John Young and Charles Duke stood on the Moon and
looked back at Earth (Figure 17). From
the lunar surface, they took a picture of Earth like none before: the
first view of our planet in far ultraviolet light (Figure 15). 23)

- This picture highlights
Earth’s ionosphere, a region of the upper atmosphere that is
mostly invisible to our eyes — aside from aurora or airglow,
if you’re in the right place at the right time — but shines
in ultraviolet, or UV, wavelengths of light. Named for the electrically
charged ions that move about freely there, the ionosphere absorbs UV
light from the Sun and re-emits it to space. The effect can be seen in
this UV image. The Sun-facing side of Earth is bright. The rest of the
planet, which is not receiving UV light from the Sun, remains dark,
shrouded in night.

Figure 16: This is a
visualization of data taken by the GOLD spectrometer aboard the SES-14
satellite. SES 14 is positioned in a geostationary orbit above
47.5º west longitude so it always observes the same hemisphere.
This data is of ultraviolet emission from Earth's ionosphere in a band
near the wavelength of 135.6 nm, an emission line of atomic oxygen
(image credit: NASA's Scientific Visualization Studio/Tom Bridgman/Joy
Ng)

- Attentive observers may notice
three strips of UV emission that extend onto Earth’s night side.
The two strips just above and below the equator are known as the
Appleton Anomaly. They mark where Earth’s magnetic field
interacts with the upper ionosphere to trigger dense fountains of
uprising plasma. The southernmost strip is UV light from the aurora
australis, or the Southern Lights.

- Launched in 2018, NASA’s GOLD
mission is now one of our key tools for ionosphere observations,
providing the first day-to-day weather measurements of the region. By
measuring far UV light, GOLD tracks changes in the ionosphere’s
ever-changing temperature, density and composition — enabling
scientists to piece together the forces that shape conditions in a part
of the atmosphere critical to many Earth-orbiting satellites and
everyday technology, including the successful transmission of radio
signals and GPS.

- This visualization of GOLD data
from March 2019 shows the transition from day to night, as well as the
Appleton anomaly, which appears as two horizontal arcs of light that
extend into night. The aurora can be seen at the top and bottom of
Earth, also extending into night.

Figure 17:
Astronaut John W. Young leaps from the lunar surface as he salutes the
United States flag at the Descartes landing site during the first
Apollo 16 extravehicular activity. Astronaut Charles M. Duke Jr., lunar
module pilot, took this picture. The Lunar Module "Orion" is on the
left. The Lunar Roving Vehicle is parked beside Orion and the object
behind Young (in the shadow of the Lunar Module) is the Far Ultraviolet
Camera/Spectrograph (image credit: NASA)

Figure 18: Dr.
George Carruthers, right, and William Conway, a project manager at the
Naval Research Institute, examine the gold-plated ultraviolet
camera/spectrograph that flew on the Apollo 16 mission. This camera
would go on to capture the first image of Earth in ultraviolet light
(image credit: U.S. Naval Research Laboratory)

• June 3, 2019: The first
release of Level 2 data from NASA’s Global-scale Observations of
the Limb and Disk (GOLD) mission is now available via the GOLD website
at http://gold.cs.ucf.edu. Information about these L2 data products is available in the updated data documentation that can be accessed at http://gold.cs.ucf.edu/documentation/

• March 12, 2019: Data from GOLD are now available from the GOLD Science Data Center (SDC).
The L1C (spatial-spectral image cubes), L1D (“Quicklook”
– thumbnail images and plots) data and relevant information about
these data can be accessed under “DATA” near the top of the
page. 24)

Figure 19: The
Quicklook data allow users to browse through GOLD L1D images for each
of the GOLD observation types performed since operations began: daytime
disk (DAY), limb scans (LIM), nighttime disk (NI1), and occultations
(OCC). Data release notes and a GOLD Science Data Products guide are
available at the “Documentation” link under
“DATA”.

Figure 20: A basic view of the
orbits and scanning profiles for ICON (in low-Earth orbit) and GOLD (in
geostationary orbit) is shown in this visualization. Here, the colors
over Earth represent model data of the density of a single ionized
oxygen atom at an altitude of 350 kilometers. Red represents high
density ( image credit: NASA GSFC’s Scientific Visualization
Studio)

• September 17, 2018: NASA's
GOLD ( Global-scale Observations of the Limb and Disk) instrument
powered on and opened its cover to scan the Earth for the first time,
resulting in a “first light” image of the Western
Hemisphere in the ultraviolet. 25)26)

- The instrument was launched from
Kourou, French Guiana, on 25 January 2018, onboard the SES-14 satellite
and reached geostationary orbit in June 2018. After checkout of the
satellite and communications payload, GOLD commissioning—the
period during which the instrument performance is assessed—began
on 4 September.

- Team scientists conducted one day
of observations on 11 September, during instrument checkout, enabling
them to produce GOLD’s “first light” image shown
here. Commissioning will run through early October, as the team
continues to prepare the instrument for its planned two-year science
mission.

- “GOLD is
an amazing technological breakthrough,” said GOLD Principal
Investigator Richard Eastes, a research scientist at LASP. “After
years of reviews, testing, testing, and more testing, the instrument is
finally making observations of the Earth. The main act has begun.
It’s a testament to the engineering and science teams, who were
responsible for building and calibrating the instrument, that
we’ve reached this significant mission milestone.”

- Along with NASA’s ICON
(Ionospheric Connection Explorer), scheduled for launch later this
fall, GOLD is a key element of NASA’s program to explore
Earth’s boundary with space, as the two missions explore this
unpredictable near-Earth region to determine how it responds to solar
and atmospheric inputs.

Figure 21:
Shown here is the “first light” image of ultraviolet atomic
oxygen emission (135.6 nm wavelength) from the Earth’s upper
atmosphere captured by NASA’s GOLD instrument. It was taken at
approximately 6 a.m. local time, near sunrise in eastern South America.
The colors correspond to emission brightness, with the strongest shown
in red and the weakest in blue. This emission is produced at altitudes
around 160 km (note how it extends above the Earth’s surface on
the horizon), when the Earth’s upper atmosphere absorbs high
energy photons and particles. The aurora, at the top and bottom of the
image, and daytime airglow, on the right hand side, are also visible.
An ultraviolet star, 66 Ophiuchi (HD 164284), is visible above the
western horizon of the Earth. Outlines of the continents and a
latitude-longitude grid have been added for reference (image credit:
LASP/GOLD science team)

- “The successful launch of
GOLD and acquisition of initial data is a fantastic result,” said
Bill McClintock, GOLD instrument scientist at LASP. “Its data
will help us understand the critical role the Sun plays in space
weather and allow us to better protect astronauts and our technological
assets that we’ve become so reliant upon in today’s
society.”

- Changes in near-Earth space can
affect our lives on Earth by disrupting the use of satellites for
communications and navigation. The result can be lost messages,
aircraft flight delays, interruptions in GPS signals, and satellite TV
outages. Incoming solar energy can also damage spacecraft electronics
and detectors, and expose astronauts to health risks from radiation.
The more we understand about the fundamental nature of our space
environment, the better we can protect these interests.

- Scientists expect to begin operations of the GOLD instrument in early October 2018.

• September 4, 2018: The
high-powered SES-14 satellite, positioned at 47.5 degrees West, is now
operational and is serving Latin America, the Caribbean, North America,
North Atlantic and West Africa. 27)

- The commercial communications
satellite also carries a hosted payload for NASA’s GOLD
(Global-scale Observations of the Limb and Disk) mission. GOLD will
provide unprecedented imaging of the Earth’s upper atmosphere
from geostationary orbit to deepen scientists' understanding of the
boundary between Earth and space.

• February 23, 2018: The
Independent Enquiry Commission formed after the Ariane 5
launcher’s trajectory deviation during its January 25, 2018
mission issued its conclusions on Thursday, February 22. The
anomaly’s cause is perfectly understood and recommendations are
clearly identified. Arianespace and ArianeGroup are immediately
implementing the Independent Enquiry Commission’s recommended
corrective measures. The current Soyuz and Ariane 5 launch campaigns
are continuing at the Guiana Space Center in French Guiana for the two
launches planned in March. 28)

During the Ariane 5 VA241
mission, carried out on January 25, 2018 from the Guiana Space Center
in French Guiana (South America), telemetry from the launcher was lost
9 minutes and 26 seconds into the flight because of a deviation in the
trajectory. Signals from the two satellites were acquired after the
nominal mission duration, and the spacecraft were confirmed to be in
good health, but in an orbit at an inclination of 20 degrees, rather
than the targeted 3 degrees. The apogee and perigee attitudes, however,
were very close to the targeted values (249 x 45,234 km.). The analysis
of data received during the first minutes of the flight, and the
reconstitution of the trajectory, confirmed that the launcher and the
flight program operated perfectly. The two satellites are now in the
process of reaching their final orbital positions, using their own
propulsion systems.

Following the launch anomaly,
Arianespace asked ESA (European Space Agency) on January 26 to set up
an Independent Enquiry Commission. Chaired by Toni Tolker-Nielsen, ESA
Inspector General, this Commission submitted its conclusions on
Thursday, February 22, 2018.

Investigations by the
Independent Enquiry Commission showed that the trajectory anomaly
resulted from an incorrect value in specifications for the
implementation of the launcher’s two inertial reference systems.
Given the special requirements of this mission, the azimuth required
for the alignment of the inertial units was 70 degrees instead of 90
degrees, as is most often the case for missions to geostationary
transfer orbit. This gap led to the 20-degree shift to the south in the
launcher trajectory from the initial seconds of flight. The cause of
the trajectory deviation, therefore, was due to a bad specification of
one of the launcher mission parameters that was not detected during the
standard quality checks carried out during the Ariane 5 launches’
preparation chain.

The Independent Enquiry
Commission’s work has highlighted the need to increase the
robustness of the control of certain data used in preparation of the
mission. Its recommendations are intended to strengthen the process of
developing and verifying the documents required for launcher
preparation and to introduce additional consistency checks.

With the cause of the anomaly
perfectly understood and corrective measures clearly identified,
Arianespace and ArianeGroup immediately implemented the recommendations
of the Independent Enquiry Commission. Applied to the current Ariane 5
launch campaign, they should enable the next flight of this heavy-lift
launcher in March 2018, following a Soyuz mission.

Stéphane Israël,
Chief Executive Officer of Arianespace, said: “I would like to
thank ESA Inspector General Toni Tolker-Nielsen, who chaired the
Independent Enquiry Commission, as well as all of its members. The
Commission was able to quickly identify the cause of the anomaly and
issue recommendations. Arianespace and ArianeGroup already are
deploying the measures recommended by the Commission, paving the way
for the next launch of Ariane 5, planned for March. Thanks to the
establishment of these corrective measures, we will be able to further
enhance the outstanding reliability of Ariane 5.”

Table 1: Results of the anomaly report of the Independent Enquiry Commission

• January 29, 2018: NASA's GOLD
mission powered on the GOLD instrument for the first time after launch
on Jan. 28, 7:23 p.m. EST. The systems engineers successfully
established communication with the GOLD instrument and its detector
doors opened when commanded. After their tests, the engineers powered
off the instrument the same day, at 7:40 p.m. EST. The instrument will
remain powered off until its host satellite, SES-14, reaches
geostationary orbit and GOLD operations commence later this year. 29)

- GOLD will investigate the dynamic
intermingling of space and Earth’s uppermost atmosphere and seek
to understand what drives change in this critical region. Resulting
data will improve forecasting models of the space weather events that
can impact life on Earth, as well as satellites and astronauts in
space.

• January 26, 2018: Both
spacecraft launched on Flight VA241 – SES-14 and Al Yah 3 –
have been acquired and are operating in orbit nominally, despite a
trajectory deviation experienced during the mission. This was confirmed
by the satellites’ operators, SES and Yahsat, respectively. 30)

- SES has informed NASA there is
minimal impact on the SES-14 satellite carrying the agency’s GOLD
instrument after a launch anomaly on Jan. 25, 2018. The satellite will
reach geostationary orbit four weeks later than originally planned. As
the spacecraft is in good health, we expect no effect on the quality of
observations and data. Originally, science operations were expected to
start in mid-October. Our partners are working to maintain that
timeline as closely as possible. We will provide updates as they become
available. 31)

GOLD (Global-scale Observations of the Limb and Disk) instrument

GOLD is a result of collaboration
among several world-leading entities. NASA/GSFC in Greenbelt, Maryland,
is providing overall NASA program management. The GOLD instrument is
being designed and built at LASP (Laboratory for Atmospheric and Space
Physics) at the University of Colorado, Boulder, CO. Richard Eastes,
the PI of UCF/FSI (University of Central Florida/Florida Space
Institute), oversees the GOLD mission. UCF will be responsible for
disseminating the data products. CU/LASP is responsible for the mission
and home of the Science Data Center for the mission. 32)33)34)

In addition to LASP, the GOLD
mission partners include NCAR (National Center for Atmospheric
Research), UCB ( University of California at Berkeley), Computational
Physics Inc. and NOAA (National Oceanic and Atmospheric
Administration). UCF is the first Florida university to lead a NASA
mission.

GOLD is a high-resolution FUV (Far
Ultraviolet) imaging spectrograph with two identical channels. The
objective is to provide global-scale imaging and limb scans, with a 30
minute cadence. GOLD will image the Earth in the far-ultraviolet from
132 to 162 nm.

The science objectives of the GOLD mission are:

• Determine how geomagnetic storms alter the temperature and composition of Earth’s thermosphere.

• Analyze the global-scale response of the thermosphere to solar extreme-ultraviolet variability.

• Investigate the significance
of atmospheric waves and tides propagating from below on the
temperature structure of the thermosphere.

• Resolve how the structure of
the equatorial ionosphere influences the formation and evolution of
equatorial plasma density irregularities.

The GOLD instrument is a dual
channel imaging spectrograph, each capable of all measurements, with a
mass of 37 kg, a power consumption of 72 W (average), a size of 40 x 30
x 70 cm, and a data rate of ~6 Mbit/s.

The GOLD imager has two identical
and independent optical channels, each capable of performing every
required measurement. These interface to the SES-14 spacecraft through
a single processor assembly, which commands each channel independently.
Images produced by the instrument are routed to a dedicated transponder
for immediate downlink to an SES ground station. The raw images are
stored at the ground station until transmission to LASP is confirmed.
These are then sent over ground line to the University of Central
Florida where high-level data processing converts the raw data into
maps of thermosphere composition and temperature. 35)

Each channel contains an ultraviolet
spectrograph equipped with an imaging detector that covers 132 to 162
nm. This wavelength range contains important emissions from the main
constituents of the thermosphere—atomic oxygen (135.6 nm) and
molecular nitrogen (the Lyman-Birge-Hopfield (LBH) band system 132
– 162 nm). Two selectable entrance slits, which are 0.2 mm and
0.4 mm wide, respectively, enable the two spectral resolutions of 0.2
nm and 0.4 nm required for measuring temperature and composition. The
optical layout of a single channel is shown here in Figure 23.

A single-mirror telescope equipped
with a plane scan mirror images the spectrograph entrance slit onto the
atmosphere. During an observation, a precision mechanism rotates the
mirror so that the slit image sweeps east-west across the Earth’s
atmosphere. The slit is only tall enough to cover a single hemisphere
(either north or south). This is accommodated by tilting the mirror
through approximately 4.5º. In this configuration, one face of the
mirror projects the slit onto the northern hemisphere and the other
face projects it onto the southern hemisphere, as illustrated in the
left panel of Figure 24. A third 2.6 mm
wide entrance slit is used for stellar occultations. In this
configuration, which is illustrated in the right panel of Figure 24,
the scan mirror is positioned near the limb of the Earth and remains
motionless as the star drifts through it. This enables GOLD to measure
the absorption of starlight by the atmosphere in order to measure the
density of molecular oxygen, which is a minor constituent of the
thermosphere.

Figure 24:
Left panel: Disk scans are performed with two swaths across the
northern and southern hemispheres, respectively. Right panel: The slit
remains motionless during stellar occultations (image credit: GOLD Team)

Figure 25: An illustration of
typical GOLD LBH emission data from a single channel for a single slit
position. On the left is an image of LBH emission intensity displayed
on a logarithmic scale in the range from 10 – 104 brightness
units. Here, the slit is positioned in the northern hemisphere near the
sub-spacecraft longitude. On the right is a display of an LBH spectrum
obtained at a single location along the slit. The actual image will
have a spectrum for each row of the detector (image credit: GOLD Team)

GOLD measures composition and temperature simultaneously:

• Two identical channels

• Each channel fully independently in all observing modes

- disk images and limb scans

- dayside: T and O/N2

- nightside: O+ density

- stellar occultations

- full disk maps and limb scans with 30 minute cadence

- limiting resolution is ~50 km

• A single channel can perform all measurements with reduced cadence or reduced spatial resolution

“GOLD’s imaging
represents a new paradigm for observing the boundary between Earth and
space,” said Bill McClintock, senior research scientist at LASP
working on the project. “It will revolutionize our understanding
of how the sun and the space environment affect our upper
atmosphere.”

The information compiled and edited in this article was provided byHerbert
J. Kramer from his documentation of: ”Observation of the Earth
and Its Environment: Survey of Missions and Sensors” (Springer
Verlag) as well as many other sources after the publication of the 4th
edition in 2002. - Comments and corrections to this article are always
welcome for further updates (herb.kramer@gmx.net).